{{Note|Much of the information in this page is duplicated at [[GTA02 GPS Problems]]; these pages should probably be merged one way or the other}}

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See GPS for details on how to evaluate the [[Neo FreeRunner GPS]] with command line utilities.

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See [[GPS]] for details on how to evaluate the Freerunner GPS with command line utilities.

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=== Problem: it takes a long time (10min+) before the FreeRunner gets first GPS data ===

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=== Problem: it takes a long time (10min+) before the Freerunner gets first GPS data ===

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It was found that the OpenMoko FreeRunner GPS has a long Time To First Fix (TTFF) with the SD card in the phone. [http://lists.openmoko.org/pipermail/community/2008-July/021774.html This thread] indicates that there is interference from the SD card slot, as without the SD card inserted it the TTFF are much shorter.

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It was found that the Openmoko FreeRunner GPS has a long Time To First Fix (TTFF) when there is an SD card in the phone. [http://lists.openmoko.org/pipermail/community/2008-July/021774.html This thread] indicates that there is interference from the SD card slot: TTFF is much shorter without an inserted SD card.

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::More specific: the GPS signal level drops by -20dBm, i.e. factor 100. Signal strength of a GPS satellite above your head is around -127dBm. Needed strength for a first fix is -145dBm with a minimum of three satellites. Once the GPS chip has a fix, it can operate at signal levels of -157dBm, thus making it possible to operate while there is data transfer from/to the SD card.

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::More specific: the GPS signal level drops by 20dB, i.e. a factor of 100. Signal strength of a GPS satellite above your head is around -127dBm. Needed strength for a first fix is -145dBm with a minimum of three satellites. Once the GPS chip has a fix, it can operate at signal levels of -157dBm, thus making it possible to operate while there is data transfer from/to the SD card.

The people of OpenMoko know about the problem and are working on it. A [http://lists.openmoko.org/pipermail/openmoko-kernel/2008-July/003777.html software workaround] is under testing. It turns off the SD card clock when the SD card is not being used. One will be able to use the SD card at the same time as the GPS except for the first approximately 30 seconds.

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{{Note|It seems that in the newer version of the hardware, a compensating capacitor is now present. So this problem should be fixed with newer devices. First noticed on 20080724 and confirmed on 20080830. You can check if it has the fix by looking for the capacitor beneath the SD card, as shown in [[Media:Gta02 gps 10pf rework sop.pdf|this PDF file]].}}

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{{Note|The capacitor also appeared on a 20080723 purchased from Pulster vendor.}}

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OpenMoko is also examining a hardware solution.

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A [http://lists.openmoko.org/pipermail/openmoko-kernel/2008-July/003777.html software workaround] has been released as a kernel patch and may be acquired simply by doing an "opkg update" and "opkg upgrade" and then rebooting your FreeRunner. This workaround effectively turns off the SD card clock when the SD card is not being used. You can then use the SD card simultaneously with GPS, except for the first approximately 30 seconds.

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Openmoko is soliciting the assistance of the community to test the effectiveness of this software fix. The experiment consists of a series of measurements in different conditions, prior to applying the software fix and then after applying the software fix. Please visit [[FreeRunner GPS Software Fix TTFF Measurement Test]] for instructions to participate and to see the results so far of this test.

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Openmoko has examined a hardware solution: soldering a 10 pf capacitor between SD card pin 5 (clk) and pin 6 (Vss) [[Image:Gta02 gps 10pf rework sop.pdf]] and more detailed [[Image:SOP_for_GPS_capacitor_rework.pdf|GPS issue SD clcok pin capacitor rework guide]]. This effectively restores GPS performance to the levels obtained without the SD card inside. The rework is not suggested to end users without hardware soldering technique and equipment. This rework is done on all the new fabricated Neo FreeRunners

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==== Hardware mod related ====

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See:

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* [[Shop:Speedevil|Speedevil's Shop]] for a UK service to perform this operation on your freerunner, or globally shipped 10pF capacitor.

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* [http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=490-1278-1-ND Digikey] for the capacitor.

=== Discussion ===

=== Discussion ===

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The following is based on [http://lists.openmoko.org/pipermail/community/2008-July/022180.html Alasal's post] to the community mailing list.

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The following is based on [http://lists.openmoko.org/pipermail/community/2008-July/022180.html Alasal's post] to the community mailing list.

;What is TTFF?

;What is TTFF?

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:This is the time to first fix of the GPS. This is the time the GPS needs to get the first clue on where you are on planet earth. So you have to do this only once. After you have a FF (first fix), you can get more fixes without any problems with the SD card in the phone.

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:TTFF means Time To First Fix of the GPS. This is the time the GPS needs to get the first clue on where you are on planet earth. So you have to do this only once. After you have a FF (first fix), you can get more fixes without any problems with the SD card in the phone.

Line 31:

Line 42:

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;Does the lower signal also effect accuracy?

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;Does the lower signal also affect accuracy?

:It is a good deal more jittery. However, if you drive around in a city you will get a lot more error from signal reflections than from the jitter.

:It is a good deal more jittery. However, if you drive around in a city you will get a lot more error from signal reflections than from the jitter.

:Wrong, you will be able to read the SD card when the GPS is on. You will probably not be able to read the SD card when you're starting the GPS (approximately 30 seconds), because the SD card only stops the GPS from getting its first fix. After that you will be able to read the SD card again.

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:Wrong, you will be able to read the SD card when the GPS is on. The clock for the SD card used to run constantly. Now the kernel turns it off when the SD card is not in use. As long as you are not constantly reading from the SD card, you should see much better first fix times. Obtaining a GPS fix does not affect SD performance.

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;Is there a better software solution?

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:Maybe. From reading the mailing list, I have understood that half the Openmoko team is looking into this bug. All this information is only 1 - 2 days old and the bug is also young, so I suspect they can fine-tune the software workaround and make it only slow down the SD card or even better.

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;Did Openmoko test the GPS with a SD card in it?

;Did Openmoko test the GPS with a SD card in it?

:Yes.

:Yes.

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;Why didn't they find it while testing the FreeRunner?

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;Whey didn't they find it while testing the Freerunner?

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:Because they have to do the tests with a fake GPS signal and with that signal it worked (In a fab you don't have a decent GPS signal). They have already modified the test, so it corresponds to the GPS signal better.

:Because they have to do the tests with a fake GPS signal and with that signal it worked (In a fab you don't have a decent GPS signal). They have already modified the test, so it corresponds to the GPS signal better.

== Information about faulty antennas ==

== Information about faulty antennas ==

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* If you removing the SD card doesn't help and you suspect your antenna, try unplugging and replugging the internal GPS connector. (See [[Disassembling_Neo1973]] about 2/3 of the way down. (this may differ on freerunner, pictures appreciated)

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* If removing the SD card doesn't help and you suspect your antenna, try unplugging and replugging the internal GPS connector. (See [[Disassembling_Neo1973]] about 2/3 of the way down. (this also applies to the Freerunner, since it's the same case)

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Also note that there is a trac ticket for this issue: [http://docs.openmoko.org/trac/ticket/1542 #1542]

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* Also note that there is a trac ticket for this issue: [http://docs.openmoko.org/trac/ticket/1542 #1542]

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[[FreeRunner_GPS_antenna_repair_SOP]] Indicates that some (rare?) units may have bad soldering, and includes a guide to fix. This will presumably void your warranty.

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* [[FreeRunner GPS antenna repair SOP]] indicates that some (rare?) units may have bad soldering, and includes a guide to fix. This will presumably void your warranty.

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[[Category:GPS]]

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[[Category:Neo FreeRunner solved GPS problems]]

Latest revision as of 12:31, 15 September 2009

See GPS for details on how to evaluate the Neo FreeRunner GPS with command line utilities.

Contents

[edit] Problem: it takes a long time (10min+) before the FreeRunner gets first GPS data

It was found that the Openmoko FreeRunner GPS has a long Time To First Fix (TTFF) when there is an SD card in the phone. This thread indicates that there is interference from the SD card slot: TTFF is much shorter without an inserted SD card.

More specific: the GPS signal level drops by 20dB, i.e. a factor of 100. Signal strength of a GPS satellite above your head is around -127dBm. Needed strength for a first fix is -145dBm with a minimum of three satellites. Once the GPS chip has a fix, it can operate at signal levels of -157dBm, thus making it possible to operate while there is data transfer from/to the SD card.

NOTE: It seems that in the newer version of the hardware, a compensating capacitor is now present. So this problem should be fixed with newer devices. First noticed on 20080724 and confirmed on 20080830. You can check if it has the fix by looking for the capacitor beneath the SD card, as shown in this PDF file.

NOTE: The capacitor also appeared on a 20080723 purchased from Pulster vendor.

A software workaround has been released as a kernel patch and may be acquired simply by doing an "opkg update" and "opkg upgrade" and then rebooting your FreeRunner. This workaround effectively turns off the SD card clock when the SD card is not being used. You can then use the SD card simultaneously with GPS, except for the first approximately 30 seconds.

Openmoko is soliciting the assistance of the community to test the effectiveness of this software fix. The experiment consists of a series of measurements in different conditions, prior to applying the software fix and then after applying the software fix. Please visit FreeRunner GPS Software Fix TTFF Measurement Test for instructions to participate and to see the results so far of this test.

Openmoko has examined a hardware solution: soldering a 10 pf capacitor between SD card pin 5 (clk) and pin 6 (Vss) File:Gta02 gps 10pf rework sop.pdf and more detailed File:SOP for GPS capacitor rework.pdf. This effectively restores GPS performance to the levels obtained without the SD card inside. The rework is not suggested to end users without hardware soldering technique and equipment. This rework is done on all the new fabricated Neo FreeRunners

The following is based on Alasal's post to the community mailing list.

What is TTFF?

TTFF means Time To First Fix of the GPS. This is the time the GPS needs to get the first clue on where you are on planet earth. So you have to do this only once. After you have a FF (first fix), you can get more fixes without any problems with the SD card in the phone.

So if we have a first fix, the SD card doesn't block the GPS anymore?

Yes, the SD card doesn't block the GPS if we have a first fix. (Some people even claim it's more stable)

Why do we need a first fix?

According to Al Johnson, the Antares4 chip on the GTA02 doesn't have the memory needed to store almanac and ephemeris, last known position or time. This means that every start is a true cold start. It is possible to save location, almanac and ephemeris at GPS shut down, and restore these information at the next startup, but that does not seem implemented yet.

Does the lower signal also affect accuracy?

It is a good deal more jittery. However, if you drive around in a city you will get a lot more error from signal reflections than from the jitter.

Wrong, you will be able to read the SD card when the GPS is on. The clock for the SD card used to run constantly. Now the kernel turns it off when the SD card is not in use. As long as you are not constantly reading from the SD card, you should see much better first fix times. Obtaining a GPS fix does not affect SD performance.

Did Openmoko test the GPS with a SD card in it?

Yes.

Why didn't they find it while testing the FreeRunner?

Because they have to do the tests with a fake GPS signal and with that signal it worked (In a fab you don't have a decent GPS signal). They have already modified the test, so it corresponds to the GPS signal better.

If removing the SD card doesn't help and you suspect your antenna, try unplugging and replugging the internal GPS connector. (See Disassembling_Neo1973 about 2/3 of the way down. (this also applies to the Freerunner, since it's the same case)

Views

Personal tools

NOTE: Much of the information in this page is duplicated at GTA02 GPS Problems; these pages should probably be merged one way or the other

See GPS for details on how to evaluate the Freerunner GPS with command line utilities.

Problem: it takes a long time (10min+) before the Freerunner gets first GPS data

It was found that the OpenMoko FreeRunner GPS has a long Time To First Fix (TTFF) with the SD card in the phone. This thread indicates that there is interference from the SD card slot, as without the SD card inserted it the TTFF are much shorter.

More specific: the GPS signal level drops by -20dBm, i.e. factor 100. Signal strength of a GPS satellite above your head is around -127dBm. Needed strength for a first fix is -145dBm with a minimum of three satellites. Once the GPS chip has a fix, it can operate at signal levels of -157dBm, thus making it possible to operate while there is data transfer from/to the SD card.

Solutions

The people of OpenMoko know about the problem and are working on it. A software workaround is under testing. It turns off the SD card clock when the SD card is not being used. One will be able to use the SD card at the same time as the GPS except for the first approximately 30 seconds.

OpenMoko is also examining a hardware solution.

Discussion

The following is based on Alasal's post to the community mailing list.

What is TTFF?

This is the time to first fix of the GPS. This is the time the GPS needs to get the first clue on where you are on planet earth. So you have to do this only once. After you have a FF (first fix), you can get more fixes without any problems with the SD card in the phone.

So if we have a first fix, the SD card doesn't block the GPS anymore?

Yes, the SD card doesn't block the GPS if we have a first fix. (Some people even claim it's more stable)

Why do we need a first fix?

According to Al Johnson, the Antares4 chip on the GTA02 doesn't have the memory needed to store almanac and ephemeris, last known position or time. This means that every start is a true cold start. It is possible to save location, almanac and ephemeris at GPS shut down, and restore these information at the next startup, but that does not seem implemented yet.

Does the lower signal also effect accuracy?

It is a good deal more jittery. However, if you drive around in a city you will get a lot more error from signal reflections than from the jitter.

Wrong, you will be able to read the SD card when the GPS is on. You will probably not be able to read the SD card when you're starting the GPS (approximately 30 seconds), because the SD card only stops the GPS from getting its first fix. After that you will be able to read the SD card again.

Is there a better software solution?

Maybe. From reading the mailing list, I have understood that half the Openmoko team is looking into this bug. All this information is only 1 - 2 days old and the bug is also young, so I suspect they can fine-tune the software workaround and make it only slow down the SD card or even better.

Did Openmoko test the GPS with a SD card in it?

Yes.

Whey didn't they find it while testing the Freerunner?

Because they have to do the tests with a fake GPS signal and with that signal it worked (In a fab you don't have a decent GPS signal). They have already modified the test, so it corresponds to the GPS signal better.

Information about faulty antennas

If you removing the SD card doesn't help and you suspect your antenna, try unplugging and replugging the internal GPS connector. (See Disassembling_Neo1973 about 2/3 of the way down. (this may differ on freerunner, pictures appreciated)